Networking protocols are normally developed in layers, with each layer responsible for a different facet for the communication. Layers exchange structured information. Each layer receives Service Data Units (SDUs) from higher layers, which are processed to generate Protocol Data Units (PDUs). Protocol Data Units are handed over to the lower layers for service. Similarly, the PDUs received from the lower layers are processed to generate SDUs, which are handed over to the higher layers. PDUs not only carry the SDUs but also carry management information that is relevant for managing the layer functionality. Defining the structure of SDUs and PDUs for a given protocol layer is critical to enable proper layer functionality. Some examples of network protocol layers include the well-known Transmission Control Protocol (TCP) and Internet Protocol (IP). The structure of TCP data units has provisions to enable end-to-end delivery. The structure of IP data units enables efficient routing.
Networks use medium access control layer (MAC) to enable coordinated access to the medium. Medium access layer uses the functionality of the physical layer (PHY) to provide services to the higher layer. MAC service to the higher layers can include guarantees on Quality of Service (QoS). QoS provides guarantees on bandwidth, latency, jitter and packet loss probability for traffic streams. Jitter refers to deviation in the time of delivery of data over the network.